Wood - used to heat more homes and for the construction of more family dwellings than any other material. That is why, from a global perspective, waste of this resource (Aggie Bonfire) is viewed as an act of ignorance. Forests cover ca. 1/5 of the earth's surface and constitute as estimated 90% of the earth's biomass. Global forest cover has decreased 19% since 1700 and crop lands have increase 466% (text table 17-1). The full ecological dynamics of this human-mediated change in the world's flora are difficult to determine but atmospheric balances, especially CO₂, are now under consideration as an element of the 'global warming' problem.

Wood defined: tissue derived from vascular cambium - secondary (not derived from a primary meristem) xylem (mostly), ray cells, and phloem. Technically, secondary xylem is present in the vascular bundles of some herbs, derived from an interfasicular cambium, but wood, in the sense of a functional product, is xylem produced by a full vascular cambium.

Sapwood vs. Heartwood:- bark (periderm) is all tissues OUTSIDE the functional vascular cylinder and secondary xylem of woody plants - it, in essence, replaces the epidermis of herbs. This includes both functional (living) and dead phloem cells, the phellogen ('cork cambium' or secondary meristem), phellem [cork] produced by the phellogen to the outside and phelloderm [soft, parenchyma tissue] produced by the phellogen toward in inside.   Also, horizontal extensions, within the functional xylem, of parenchma cells to produce conducting (horizontal) rays within the wood.

Hardwoods = dicots with many cell types in xylem [ray,vessel elements, phloem, tracheids

Softwoods = gymnosperm wood = mostly tracheids

annual rings - different rate of cambial cell divisions [and cell sizes] as a function of the annual cycle and also variation between growing seasons - DENDROCHRONOLOGY

Wood Characteristics: (see overview of taxonomic variation):

    Porosity:  arrangement of the vessel elements within a given annual ring (dicot wood)

    Grain:  alignment of the vessel elements (parallel to the vertical axis of the tree, tipped relative to this axis, spiral, etc.

    Figure:  visual aspect of the wood determined by number and size of rays, porosity (hardwoods), arrangement of the annual rings and presence/absence of lateral branch extensions through the xymel ('knots') or unusual growths resulting from cambial disfunction ('burl')

    Density:  mass divided by volume (1 cm³ - oven dried) - balsa (Ochroma - Bombacaceae) is less dense than water whereas Lignum vitae (Guaiacum - Zygophyllaceae) is the hardest and most dense commerical timber.

Wood Products:

Veneers - thin sheets produced by shaving from a flat surface or (more often) by rotary 'peeling' - use mostly for covering and plywood production.

Particle Board/Fiberboard - stimulated by availability of synthetic resins and decline of large trees for milling.

Paper -  Modern paper production is based on separation and recombination of plant fibers.  This process began in China (maybe 2,000 years ago) using hemp and flax fibers.  Egyptian papyrus was formed by pressing together sheets derived from leaves of Cyperus papyrus (Cyperaceae) and, while based on fibrous material derived from plants, not 'true' paper.  The process of paper making moved slowly from Asia to Europe but hand labor and limited fiber sources (linen, cotton, hemp).  The French mechanized the process in the late 1700s and the focus turned to wood fibers in the mid-1800s due to procedural innovation (also French) for separating wood fibers.

    sulfite process:  wood chips cooked in a digester with bisulfites, hot acid added, softened fibers blown to separate

    sulfate process:  digestive agents (sodium sulfate, sulfide, hyroxide) different but 'acid free' processing extends life of paper and gymnosperm resins are removed - thus, this is most common modern process

Rayon/Cellophane - direct chemical conversion of pure cellulose derived from wood fibers

Acetate/Acetate fibers - acetyl groups added to pure, plant-derived cellulose - mostly wood pulp but also 'linters' (small trichomes) from cotton seeds

Commercial utilization of wood products stimulated global deforestation that has progressed to the point that 'old growth' forests are a rarity, especially in North America.  The long term impact of this human-mediated change in the world's ecology is unknown.